Safety glazing or penetration resistant glazing for structural items such as windows, windshields and the like utilizing polycarbonate or polysiloxane-polycarbonate with resinous layers as their structural components are well known Glass-polycarbonate resin laminates are disclosed in U.S. Pat. No. 3,666,614, the glass and polycarbonate being sealed or joined together by an ethylene-vinyl acetate copolymer. In U.S. Pat. No. 3,520,768, there are disclosed laminates of relatively thick glass utilizing a thin polycarbonate foil disposed between glass sheets as the cohering material. In addition, there are known laminates wherein self-healing, chemically resistant polyurethane films or layers are adhered to glass, as for example, in U.S. Pat. No. 3,979,548. Moreover, there are also known, as disclosed in U.S. Pat. No. 4,027,072, laminates comprising polycarbonates and glass or polysiloxane-polycarbonate block copolymers, described more particularly hereinafter as the adhesive, and glass in various combinations and in which an ultraviolet, mar resistant, hard coat is utilized on at least one external surface or both external surfaces of such laminates. These last-mentioned laminates are particularly useful in structural items such as bullet resistant glass, windshields, windows and as transparencies for gas masks and the like. It is normal practice in constructing certain of such laminates to utilize glass or relatively hard solid resinous materials as the impact shock receiving layers while utilizing polycarbonate as the back or inner or downstream layer or that presented to the person or object being protected. In those cases where polycarbonate is used as a layer of a laminate, it is often, because of the relative softness of the polycarbonate, protected, especially on its exposed surface, with a mar- or scratch-resistant and transparency preserving layer usually less than 2 mils thick and preferably from about 0.05 to 1 mil thick. The minimum thickness is restricted only by application technology and the desired durability of the mar-resistant coating. Maximum acceptable coating thickness is a function of the relative brittleness of the mar-resistant finish. The inner surface can also be so coated to prevent marring during lay-up and the like. In general, such mar-resistant layers, which are well known, can be metal oxides; modified melamines; ultra-violet hardenable organics such as acrylated monomers or mixtures of these monomers with acrylate-modified polymeric resins; inorganic glasses such as silica or alumina; polyurethanes; filled and unfilled silicone resins with recurring organic groups such as polymethyl methacrylate; polyamide ester resins; and ion-beam deposited carbon, and all of which, among others are harder and relatively more brittle than the underlying polycarbonate layer which they protect. It was found, however, that in impact shock-resistant laminates utilizing such relatively brittle layers along with polycarbonate, the relatively brittle material cracks under impact causing the polycarbonate layers and particularly the rear-most polycarbonate layer to spall, causing damage to exposed objects behind the laminate. Such spalling occurs because of the so-called "notch sensitive" character of polycarbonates. Thus, if an overlying brittle layer is broken, the fracture lines propagate to the polycarbonate and act as "critical" notches causing the polycarbonate to fail in a brittle manner with little of the energy absorption typical of this normally impact-resistant material.
Such disadvantages were overcome by providing impact shock resistant laminates using polycarbonate and overlying relatively more brittle material of specific thicknesses, thus achieving laminates which exhibit reduced notch sensitivity and thereby making them more useful from a practical point of view.
It is to be noted, however, that although the known laminates are useful in many areas such as, for example, those mentioned, they still present certain disadvantages even though they are characterized by superior penetration and spall resistance as well as being relatively light in weight and having good clarity, strength and integrity over a wide range of temperatures. For example, these known laminates are relatively thick and very often, after prolonged use asymmetrical glass/polycarbonate laminates, in particular, show evidence of swelling, stress cracking, and even delamination. Furthermore, in such laminates which utilize polycarbonates, interlayers of adhesive are generally necessary for bonding the polycarbonates to glass or other structural materials. However, the interlayers or adhesives employed often have low adhesion to polycarbonates or are incompatible therewith, thus resulting in delamination, hazing and stress cracking.
Consequently, there exists a need for improved impact or shock resistant laminates which exhibit superior penetration and spall resistance and which, at the same time, are relatively thin, light in weight and have good clarity, strength and integrity over a wide range of temperatures and which at the same time provide abrasion, chemical and permeation resistance. The present invention provides such materials or laminates.